In a cooling system of an internal combustion engine, there is a radiator supporting a catalyst. The catalyst purifies harmful matter such as ozone in atmosphere. In specific countries and regions, a vehicle mounting a radiator provided with an ambient air purifying function is given a favorable treatment in which an exhaust gas regulation is relaxed.
However, the radiator having the ambient air purifying function is more expensive than a general radiator. Thus, when the radiator having the ambient air purifying function is broken, there is a possibility to conduct an unauthorized alteration in which the radiator having the ambient air purifying function is changed into a cheap radiator having no ambient air purifying function. If such an unauthorized alteration of the radiator is conducted, it is necessary to detect the unauthorized alteration early and notify the driver by a warning lamp.
U.S. Pat. No. 6,695,473B2 shows that a temperature sensor is fixed at a vicinity of a coolant inlet of the radiator having the ambient air purifying function by a non-removable means. The temperature sensor cannot be removed unless the temperature sensor is broken. In this system, it is monitored whether a detection value of the temperature sensor indicates a similar behavior to a detection value of a coolant temperature sensor. By determining whether the temperature sensor is properly fixed on the radiator, it is determined whether the unauthorized alteration is conducted.
However, in a technology shown in U.S. Pat. No. 6,695,473B2, it may be happen that the temperature sensor fixed on the radiator having the ambient air purifying function is cut away and fixed on the coolant passage or a cylinder head. The detection value of the temperature sensor is made up to show a similar behavior of the coolant temperature sensor, and the radiator is changed into cheap radiator. When such an unauthorized alteration is conducted, since the detection value of the temperature sensor indicates a similar behavior of the detection value of the coolant temperature sensor, an unauthorized alteration can not be detected.
Furthermore, in U.S. Pat. No. 6,695,473B2, when a temperature sensor is fixed on the normal radiator, it is necessary to fix the temperature sensor at a vicinity of a coolant inlet in such a manner that a detection value of the temperature sensor indicates a similar behavior of the detection value of the coolant temperature sensor. Thus, a fixing position of the temperature sensor is limited to a narrow area at a vicinity of the coolant inlet, and it may be difficult to fix the temperature sensor smoothly.